Which of the following represents the countercurrent mechanism in fish?
Which of the following represents the countercurrent mechanism in fish?
The correct option is B 2
"Countercurrent" is literally a current flowing in a direction opposite to another. The second diagram here, represents countercurrent mechanism, so called because the blood and water flow in opposite directions, making respiration in fishes efficient. When the water enters in through the mouth, it is richly oxygenated. Let us assume it has 100 ppm of oxygen in it. By the time it reaches the other end, through the gills, it would have given up much of its oxygen to the blood, and the level of oxygen would have dropped to, say, 20 ppm. Now the blood, which is flowing in the opposite direction has 20 ppm of oxygen, and as it flows, it gains oxygen, and by the time it reaches the opening of the operculum where water enters, it would have gone up to 80 ppm. Thus, in this countercurrent mechanism, there is a constant gradient that is created which helps oxygen diffusion to happen more effectively. In the case of diagram 1, since the blood and water flow in the same direction, both blood and water would have the same concentration of oxygen, which means that there is no gradient created, for diffusion to take place.
2
"Countercurrent" is literally a current flowing in a direction opposite to another. The second diagram here, represents countercurrent mechanism, so called because the blood and water flow in opposite directions, making respiration in fishes efficient. When the water enters in through the mouth, it is richly oxygenated. Let us assume it has 100 ppm of oxygen in it. By the time it reaches the other end, through the gills, it would have given up much of its oxygen to the blood, and the level of oxygen would have dropped to, say, 20 ppm. Now the blood, which is flowing in the opposite direction has 20 ppm of oxygen, and as it flows, it gains oxygen, and by the time it reaches the opening of the operculum where water enters, it would have gone up to 80 ppm. Thus, in this countercurrent mechanism, there is a constant gradient that is created which helps oxygen diffusion to happen more effectively. In the case of diagram 1, since the blood and water flow in the same direction, both blood and water would have the same concentration of oxygen, which means that there is no gradient created, for diffusion to take place.
